1. Field of Invention
The current invention relates to security tags and more particularly, discloses a security tag that can be removed from an article to which it is attached by transmission of a wireless (e.g., radio frequency) signal to the tag.
2. Description of Related Art
Electronic article surveillance (EAS) security tags, typically comprise a resonant circuit that utilizes at least one coil and at least one capacitor that operate to resonate when exposed to a predetermined electromagnetic field (e.g., 8.2 MHz) to which the EAS tag is exposed. Scanning equipment transmits a signal at the frequency of the tag and detects the signal created by the resonant circuit. Such tags are applied to merchandise to prevent theft and for inventorying. Various different resonant tag products are commercially available and described in issued patents, for example, U.S. Pat. Nos. 5,172,461; 5,108,822; 4,835,524; 4,658,264; and 4,567,473 all describe and disclose electrical surveillance tag structures.
One form of EAS tag is known as a “hard tag.” A hard tag is typically a reusable device that contains the resonant circuitry and that can be attached to an article with means for keeping the tag attached until released by a special apparatus. By way of example only, the coil and the capacitor are enclosed in a first device having a retaining device to accept a pin. A second device containing a pin and looking like a large thumb tack can be inserted through an article of clothing, for example, and into the retaining device of the first device. In an exemplary design the pin is retained by a ball clutch in the tag that prevents removal once the pin is inserted. In this manner, the hard tag is affixed to an article and remains attached such that it cannot be removed by a customer. In typical prior art hard tags having a ball clutch, pressure is applied to the balls by an iron slug backed by a spring. Upon application of a large magnetic field at a point of sale, the slug retracts, relieving pressure from the ball clutch, allowing the pin to be removed by store personnel.
Another type of RF security device is an RFID device. Such a device contains active circuitry to produce an encoded RF signal when energized by an external RF signal. Circuitry for an RFID device can also be contained in a hard tag as described above.
One problem with magnetically-releasable hard tags is that thieves sometimes carry magnets strong enough to remove the tags. Another problem is that of untrustworthy store personnel, who remove the tags for an accomplice customer, without the customer ever paying for the item. Thus, there exists a need for an EAS or RFID hard tag with a more secure removal mechanism.
The present invention is a hard tag powered by harvesting ambient radio frequency energy with circuitry that allows removal only upon application of an encoded RF signal at the appropriate frequency. Such a device prevents thieves from removing the hard tags, and, when linked to a system which tracks an article identification number for each time the RF signal is applied to allow release of a hard tag, can be used to track removal of tags by store personnel.
All references cited herein are incorporated herein by reference in their entireties.